Liquid crystal polarization interference element, optical filter, and optical system

Abstract

A liquid crystal polarization interference element is provided that suppresses fluctuation in the wavelength at which maximum transmittance occurs, even when light is incident at an oblique angle. The element includes two or more sets of liquid crystal layers, each set having a first liquid crystal layer and a second liquid crystal layer. Each of the first and second liquid crystal layers includes a liquid crystal layer R formed by immobilizing horizontally aligned rod-like liquid crystal compounds and a liquid crystal layer D formed by immobilizing vertically aligned disk-like liquid crystal compounds. The liquid crystal layer R and the liquid crystal layer D have parallel slow axes and equal in-plane retardations, and the first liquid crystal layer and the second liquid crystal layer have in-plane slow axes that intersect each other. An optical filter including the liquid crystal polarization interference element is also provided.

What is claimed is: 
     
         1 . A liquid crystal polarization interference element comprising:
 two or more liquid crystal layer sets in a thickness direction, each set consisting of a first liquid crystal layer and a second liquid crystal layer,   wherein the first liquid crystal layer includes at least one liquid crystal layer R 1  formed by immobilizing horizontally aligned rod-like liquid crystal compounds, and at least one liquid crystal layer D 1  formed by immobilizing vertically aligned disk-like liquid crystal compounds,   the second liquid crystal layer includes at least one liquid crystal layer R 2  formed by immobilizing horizontally aligned rod-like liquid crystal compounds, and at least one liquid crystal layer D 2  formed by immobilizing vertically aligned disk-like liquid crystal compounds,   an in-plane slow axis of the liquid crystal layer R 1  and an in-plane slow axis of the liquid crystal layer D 1  are parallel to each other,   an in-plane slow axis of the liquid crystal layer R 2  and an in-plane slow axis of the liquid crystal layer D 2  are parallel to each other,   the in-plane slow axis of the liquid crystal layer R 1  and the in-plane slow axis of the liquid crystal layer R 2  intersect with each other,   a sum of in-plane retardations of the liquid crystal layers R 1  and a sum of in-plane retardations of the liquid crystal layers D 1  are equal to each other, and   a sum of in-plane retardations of the liquid crystal layers R 2  and a sum of in-plane retardations of the liquid crystal layers D 2  are equal to each other.   
     
     
         2 . The liquid crystal polarization interference element according to  claim 1 ,
 wherein an in-plane retardation of the first liquid crystal layer and an in-plane retardation of the second liquid crystal layer are equal to each other.   
     
     
         3 . The liquid crystal polarization interference element according to  claim 1 ,
 wherein the in-plane slow axes of all of the liquid crystal layers R 1  are parallel to each other and the in-plane slow axes of all of the liquid crystal layers R 2  are parallel to each other, and   the in-plane retardations of all of the first liquid crystal layers are equal to each other and the in-plane retardations of all of the second liquid crystal layers are equal to each other.   
     
     
         4 . The liquid crystal polarization interference element according to  claim 1 ,
 wherein an in-plane slow axis direction of the liquid crystal layer R 1  of the first liquid crystal layer and an in-plane slow axis direction of the liquid crystal layer R 2  of the second liquid crystal layer in the liquid crystal layer sets arranged on both sides in the thickness direction and the liquid crystal layer set arranged in a central part in the thickness direction are different from each other, and   in-plane retardations of the first liquid crystal layer in the liquid crystal layer sets arranged on both sides in the thickness direction and the liquid crystal layer set arranged in the central part in the thickness direction are different from each other.   
     
     
         5 . The liquid crystal polarization interference element according to  claim 1 ,
 wherein the liquid crystal layer R 1  and the liquid crystal layer D 1  of the first liquid crystal layer and the liquid crystal layer R 2  and the liquid crystal layer D 2  of the second liquid crystal layer include an infrared absorbing colorant.   
     
     
         6 . The liquid crystal polarization interference element according to  claim 1 ,
 wherein the liquid crystal layer R 1  and the liquid crystal layer D 1  of the first liquid crystal layer and the liquid crystal layer R 2  and the liquid crystal layer D 2  of the second liquid crystal layer include a liquid crystal elastomer.   
     
     
         7 . A liquid crystal polarization interference element comprising:
 two or more liquid crystal layer sets in a thickness direction, each set consisting of a first liquid crystal layer and a second liquid crystal layer,   wherein the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer R including a rod-like liquid crystal compound,   the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer D including a disk-like liquid crystal compound,   an in-plane slow axis of the first liquid crystal layer and an in-plane slow axis of the second liquid crystal layer intersect with each other, and   a sum of in-plane retardations of the first liquid crystal layers and a sum of in-plane retardations of the second liquid crystal layers are equal to each other.   
     
     
         8 . The liquid crystal polarization interference element according to  claim 7 ,
 wherein the liquid crystal layer R and the liquid crystal layer D include an infrared absorbing colorant.   
     
     
         9 . The liquid crystal polarization interference element according to  claim 7 ,
 wherein the liquid crystal layer R and the liquid crystal layer D include a liquid crystal elastomer.   
     
     
         10 . An optical filter comprising, arranged in the following order:
 a first polarizer;   the liquid crystal polarization interference element according to  claim 1 ; and   a second polarizer.   
     
     
         11 . The optical filter according to  claim 10 ,
 wherein the first polarizer and the second polarizer are provided to sandwich the liquid crystal polarization interference element in a thickness direction.   
     
     
         12 . The optical filter according to  claim 10 ,
 wherein the first polarizer and the second polarizer are arranged such that transmission axes of the two polarizers are orthogonal to each other.   
     
     
         13 . The optical filter according to  claim 10 ,
 wherein the first polarizer and the second polarizer are arranged such that transmission axes of the two polarizers are parallel to each other.   
     
     
         14 . The optical filter according to  claim 10 , further comprising:
 a retardation layer between at least one of the first polarizer or the second polarizer, and the liquid crystal polarization interference element,   wherein an in-plane slow axis of the retardation layer and an absorption axis of any of the first polarizer and the second polarizer are parallel to each other.   
     
     
         15 . An optical system comprising:
 a light source unit;   the optical filter according to  claim 10 ; and   a light receiving section.   
     
     
         16 . The optical system according to  claim 15 , further comprising:
 a condenser lens.   
     
     
         17 . The optical system according to  claim 15 , further comprising:
 a beam splitter.   
     
     
         18 . The optical system according to  claim 15 , further comprising:
 a light guide element.   
     
     
         19 . The optical system according to  claim 15 ,
 wherein the optical filter and the light receiving section are adjacent to each other.   
     
     
         20 . The optical system according to  claim 19 , further comprising:
 a plurality of the optical filters having different central wavelengths of transmitted light.